1. Field of the Invention
The present invention relates to the field of aviation technology, particularly, to the structure of air intakes designed for air-jet engines of supersonic flying vehicles with an expanded speed range.
2. Description of the Prior Art
An air intake is known which comprises a supersonic zone with a flat surface of supersonic flow braking, this surface being adjacent to the fuselage surface via a boundary layer deflector, a throat, and a subsonic zone, as, for example, in a Russian aircraft SU-27 (Technical Information of the TsAGI (Tsentralni Aero-Gidrodinamicheski Institut, Institute of Aeronautical Research) xe2x80x9cNews of Foreign Science and Technologyxe2x80x9d, Issue 2-3, 1994). In a subsonic flight regime, the air intake throat should be expanded, and in a supersonic regime it should be converged. The channel geometry is changed with a complex automatic control system comprising, in particular, a drive for movable panels of the air intake. To provide for aerodynamic stability of the air-jet engine, the field of the air flow which is formed by the air intake should be sufficiently uniform.
With this object in view, an attempt is usually made to construct the air intake channel containing no curves where centrifugal forces can be generated. As a result, the structure becomes more complex. For example, the power installation of the flying vehicle nose becomes raised above the horizontal plane. The designed supersonic regime of such an air intake is characterized by the fact that the supersonic flow shocks are on the front edge of the cowl, the air flow rate ratio is approximately equal to 1.0, and the drag is minimal.
When the Mach number of the incoming flow is less than a designed one, the shock inclination is decreased, a portion of the flow passes into a free space, the entrapped small jet of air has a cross section area which is less than that of the entry, and the air intake drag is increased. When the Mach number of the incoming flow is greater than the designed one, the shocks pass inside, the cross section air of the small decelerated jet becomes less than the entry surface area, and a portion of a non-decelerated flow passes into the air intake, this portion increasing with the increase in the excess of the flow speed over the designed one. The recovery ratio of the full pressure of the air intake is decreased accordingly.
The optimum degree of compression (the so-called external compression) of the flow in front of the entry whose boundary is beyond the front edge of the cowl is determined by comparing a gain obtained due to the increase in the recovery ratio and a loss caused by the increase in the wave drag of the cowl whose profile matches the current surface of the inner field. For this reason such air intakes are used at a Mach number of up to 2.2 . . . 2.5. A mixed (internal+external) compression is employed for greater Mach numbers. However, since the maximum degree of internal compression, that is, the relative channel convergence, is determined by the condition that the air intake will be started at a minimum Mach number from the rate of operating conditions, this degree is also rather small and it is usually increased by using a structurally complex forcible control of air intake.
The known side intake which is selected as a prototype (Patent of Russian Federation No. 2078717) comprises a supersonic braking surface placed outside into a free incoming flow having no boundary layer, this surface turning the flow toward the fuselage, thereby making it shorter and lighter. The air intake cowl is located behind the fuselage boundary layer deflector. As a result, the above-mentioned limitations relating to the increase in the wave drag on the cowl are lifted. If such an intake has a folded structure, the degree of internal compression can be increased by starting the air intake during its opening, in addition to resolving the extraneous problem of decreasing the size of the propulsion system in a transportation position.
The drawback of such air intakes, which reduces its efficiency and reliability, especially, in a regime with Mach numbers less than the designed ones, is that they have a small range and degraded characteristics in an off-design regime and lack auto start in case of accidental stall at low Mach numbers. The restart requires the installation of a servo system with a braking surface drive that, as any complex system, has low reliability and a nonzero actuation time.
It is a technological object of the present invention to increase the efficiency and reliability of supersonic air intake operation in an expanded flight speed range by increasing the flow rate and full pressure recovery ratios, decreasing the drag, and providing for auto start in case of accidental stalls in the whole range of operation Mach numbers.
In order to attain this object, it is suggested to modify the structure of an air intake comprising a supersonic zone with an optionally tiltable braking surface, a throat, and a subsonic zone by introducing at least one additional air flow channel close to the main air flow channel and installing an additional surface (panel) at the entry of this additional air flow channel, which is located in the supersonic zone, this additional surface being free to turn around an upstream rotation axis located at the channel side which is far from the intake cross section center.
At the exit of the additional channel, which is located in the subsonic zone, there can be installed a check valve in the form of another tiltable panel improving the aerodynamics of the subsonic channel and having through slots for transmitting the increased pressure to the first panel and boundary-layer bleeding.
The additional braking panel can close the exit into the additional channel in a non-airtight manner so that the slots form a nozzle for blowing air into the boundary layer in order to implement the conventional method for boundary layer control.
In order to increase the degree of freedom in designing an air intake by affecting the turning of the additional panel located in the supersonic zone and thereby affecting the air intake characteristics in a transition period, the rear surface of the additional panel can rest on the exit of a special channel whose entry is located in one or another portion of the subsonic zone with a positive pressure gradient.
In order to air-tight seal the lateral slots between the movable additional panel and stationary side webs of the air intake, a gasket can he installed at the side end faces of the movable panel. The gasket is pressed to the side wall as the air pressure increases and can be in the form of an expandable pipe having orifices for pumping which are located in the increased pressure zone at the rear side of the additional braking panel.
In case of a minimum Mach number from the range of operation regimes, the additional panel is in the lowered position owing to the increased pressure of a flow that was turned around on the opposite surface. In this position, the additional panel opens the entry of the additional channel, thereby expanding the intake throat to the size corresponding to the lower value of the Mach number. As the flying vehicle is accelerated, the shocks increase their inclination and get off the additional braking surface, thereby freeing it from the increased pressure from the outer side (a zone of the expanding supersonic Prandtl-Meier flow with a reduced static pressure is formed thereon). In this case, the additional panel takes, according to the designer selection, either a position along the flow lines or that of a wedge braking a free incoming flow, under the effect of an optional spring and the increased pressure transmitted via the boundary layer which is evolving to a separation stage and/or via an optional special channel from the increased pressure zone of the subsonic channel (as the throttling of the air intake creates the respective counterpressure). As this takes place, the additional panel closes the entry of the additional channel for the non-decelerated flow, thereby reducing the throat size to a level corresponding to a greater value of the Mach number and serving as a check valve preventing the outflow of air from the increased pressure zone. When a wider range of Mach numbers is employed, several additional channels can be formed. In this case, however, care should be exercised to see that the surface area of the throat corresponding to lower Mach numbers provides for start.
Thus, the air intake efficiency increases owing to the increase in the degree of internal compression and, therefore, in the full pressure recovery ratio, and also because the xe2x80x9cdesignedxe2x80x9d Mach number of the air intake is not a single Mach number usually selected in the middle of the operation range, but a set of Mach numbers starting from the minimum Mach number, which results in the entrapped air jet always having a surface area equal to the entry surface area in this range and, consequently, having no flow drag.
The increase in the air intake reliability can be explained as follows. If the counterpressure behind the throat is accidentally increased, thereby causing the separation of flow accompanied by the expulsion of the normal shock beyond the inlet plane, the tiltable additional brake surface and the additional counterpressure valve, provided it is installed, start to operate as vanes, should they be brought into the uniform subsonic flow, and completely open the additional throat and prepare the throat for the restart of the air intake upon the release of the increased counterpressure. This allows the surge margin to be reduced and enables a safe operation in a higher point of the throttle characteristic of the air intake.
The comparison with the prototype demonstrates that the apparatus in accordance with the present invention is characterized by the fact that it has at least one additional channel with its own tiltable brake surface at the entry and, optionally, a counterpressure valve at the exit which automatically change the configuration of the flow channel of the air intake according to the current Mach number of the flight and the counterpressure value in the subsonic channel.
Therefore, a conclusion can be made that the claimed technical resolution of the problem of braking a supersonic air flow with a minimum loss of full pressure, flow rate, and external resistance within a wide range of supersonic Mach numbers conforms to the xe2x80x9cnoveltyxe2x80x9d criterion. A straightforward approach to the resolution of this problem in similar air intakes based on a forcible control (included in an automatic engine control system) of the panels of the main braking surface is structurally more complex, involves the usage of a large amount of materials, and results in a slower response than the claimed one. This suggests that the claimed technical solution is nonobvious, and a conclusion can be made that it conforms to the xe2x80x9cinventivenessxe2x80x9d criterion.